Optimizing brachytherapy for locally advanced cervical cancer

Int. J. Radiation

Oncology

Pergamon

Biol. Phys., Vol. 29. No. 4. pp. 873-877. 1994 Copyright (c: 1994 Elsevier Science Ltd Printed m the USA. All rights reserved 0360-30 16194 $6.00 + .OO

0360-3016(94)EOO15-C

??Technical Innovations and Notes

OPTIMIZING

BRACHYTHERAPY

CHARLES G. J. H. NI~~L, M.D.,*

FOR LOCALLY ADVANCED CERVICAL CANCER

PETER C. M. KOPER,

M.D.,*’ ANDRIES G. VISSER, PH.D.,+

DICK SIPKEMA* AND PETER C. LEVENDAG, M.D.,

PHD.*

Dr. Daniel den Hoed Cancer Center, Departments of *Radiation Oncology and +Clinical Groene Hilledijk 301, 3075 EA Rotterdam, The Netherlands

Physics,

Purpose:No adequate highdoseratebrachytherapy technique existsto cover all known tumor volume by using one type of applicator in patients presenting with a cervix carcinoma extending to the vaginal wall and the parametria. Methods and Materials: We adapted the existing high dose rate applicator, existing of two ovoids and one intrauterine tube, to achieve adequate irradiation of the uterus, the parametria, and the vaginal wall in these patients. Using the optimization program of the Nucletron Planning System, isodose curves were obtained to apply a specified dose of 8.5 Gy at point A and at 5 mm depth of the vaginal wall by using a single applicator for both fractions. Results: Fractionated high dose rate brachytherapy can be given with both higher dosimetric accuracy and more adequate irradiation of the vaginal and the parametrial tumor component after adapting the existing high dose rate applicator for brachytherapy in cervical cancer.

Cervical cancer, Locally advanced, Radiotherapy,

Brachytherapy.

METHODS

INTRODUCTION

Accepted for publication 4 January 1994. ’On behalf of the (DDHCC) Radiation Oncology Gynecology Group.

requests

to: Peter C. M. Koper. gratefully thank Mrs. I. K. Kolkmanfor her criticism on the dose optimization and Ms. I. for her help in preparing the manuscript.

Acknowledgements-We Deurloo Dijkstra

MATERIALS

In the DDHCC, brachytherapy for cervical carcinoma is applied as a booster dose after external irradiation. It consists of two applications of 8.5 Gy each (HDRmicroSelectron) at point A. A detailed description of the technique was presented by Subandono (5). In brief, this applicator exists of two ovoids and an intrauterine tube. A rectal retractor is positioned to lower the rectal dose, to reduce the rectal complication rate. The applicator is fixed by a long monodenticular tenaculum firmly attached to the posterior lip of the cervix. All parts are interconnected outside the patient with one fixation screw (Fig. 1). Dwell positions of the step-wise moving single iridium point source are defined in the intrauterine part (length 40-70 mm) of the central-and in the ovoids of the two lateral tubes. The maximum distance between the center of the vaginal segment of the intrauterine tube and the surface of the ovoids is 18.5 mm. Two teflon semicylindrical parts were constructed with a radius of 18.5 mm each, to assure a constant distance between the vaginal

In patients presenting with a cervix tumor with vaginal, as well as parametrial extension, high dose rate (HDR) brachytherapy in the Dr. Daniel den Hoed Cancer Center (DDHCC) consists of one application of the classical “pear-shaped” irradiation volume with the applicator as developed in Rotterdam (two ovoids and one intrauterine tube), followed by one application of a “banana-shaped” irradiation volume using an intrauterine tube only, with dwell positions of the iridium HDR point source in the intrauterine, as well as in the vaginal part of the tube. This treatment method is unsatisfactory because of the inevitable underdosage of the parametria (irradiated in the first application only) and the vagina (irradiated in the second application only) and because of the dosimetric inaccuracy resulting from combining two applicator types. A boost with external beam therapy results in similar uncertainties. We, therefore, adapted the existing HDR applicator to irradiate the uterus, the parametria, and the vaginal wall with one applicator configuration only.

Reprint

AND

873

814

I. J. Radiation Oncology 0 Biology 0 Physics

Fig. 1. Rotterdam

applicator

with rectal retractor

wall and the vaginal dwell positions. A rectal retractor was made such that a constant distance of 18.5 mm between the posterior wall of the vagina (adjacent to the rectal retractor) and the vaginal dwell positions is achieved. In this way, the vagina is filled with a “cylinder” consisting of three different parts of the applicator: the vaginal tubes of the ovoids (anterior), the two semicylindrical teflon parts (middle), and the rectal retractor (posterior) with a radius of 18.5 mm between the center of the vaginal segment of the intrauterine tube and the surface of the vaginal mucosa (Fig. 2). The existing applicator is to be inserted in the usual way (5). The specially constructed rectal retractor is positioned. After this, the two teflon semicylinders are brought together extracorporally so that the ovoid catheters are situated anterior and the rectal retractor is positioned posterior to the teflon pieces. The cylinder is slid over the vaginal segment of the intrauterine tube until its top is adjacent to the ovoids. Finally, the bladder chain and the rectal plug are introduced (5) (Fig. 3). The dose was prescribed to the 8.5 Gy isodose line of the “pear-shaped” irradiation volume of the existing applicator, thereby extending the 8.5 Gy coverage of the target volume to the part of the vagina at risk for tumor

* HDR-microselection Netherlands.

Rotterdam

applicator,

Nucletron,

The

Volume 29, Number 4, 1994

and vaginal teflon semicylinders

separated.

recurrence. This was realized by adding dwell positions in the vaginal segment of the intrauterine tube (to be loaded with the radioactive iridium point source over the length of the vagina where tumor may recur). Dose points describing the 8.5 Gy isodose curve of the existing tandem applicato? were entered in the Nucletron Planning System (one dose point for every third intrauterine or ovoid dwell position); additional dose points at a distance of 23.5 mm of the vaginal dwell positions were entered (two dose points for every vaginal dwell position) (Table 1). Point A was entered as a point relative to the applicator [defined in the Manchester system (6)]. The relative weights of the dwell positions were calculated by the optimization program of the Nucletron Planning System (optimization on dose points, distance implant) (Table 2). The reference dose of 8.5 Gy was specified in point A. This resulted in an 8.5 Gy isodose line through the described dose points at the vagina, the parametria, and the uterus (Fig. 4). DISCUSSION Tumor extension of cervical cancer to the vagina and the parametria is not very common. Inadequate brachytherapy in these patients decreases local control rates, as

Brachytherapy for cervical cancer 0 C. G. J. H. NIEL et ul

Fig. 2. Complete

shown by Perez (3). He clearly established a dose relationship in Stage IIB and Stage III patients between the dose in the medial parametrium (as given by brachytherapy) and the local control rate. No such relationship was detected in patients with less tumor extension. In the DDHCC, the parametrial/uterine dose in patients without vaginal tumor extension is 8.5 Gy in point A. This dose is given twice with a l-week interval. The vaginal

Fig. 3. Applicator

875

applicator.

dose per fraction in case of a cervical tumor with extension to the vagina is 8 Gy at 5 mm depth from the surface of the vaginal mucosa; two fractions with a l-week interval are applied. For both types of applicator, an acceptable 5% rectal complication rate and absence of bladder complications were found. Until now, in the DDHCC, HDR brachytherapy, for cervical cancer extending to the vagina and the parametria,

inserted

(lateral view).

876

I. J. Radiation Oncology 0 Biology 0 Physics Table 1. Dose distribution through used for optimization

Applicator points Point

1

Dose distribution X 20.0

Dose points

Y -20.0

Z

Percent

0

100

Dose distribution

Point

x

Y

Z

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

-30.3 30.2 -0.4 -0.4 -0.4 -0.4 -0.3 -0.2 -23.1 -23.1 -23.2 -23.2 -23.2 -23.3 -23.3 -23.4 -23.4 -23.5 22.9 22.9 22.8 22.8 22.8 22.7 22.7 22.6 22.6 22.5

12.2 12.0 -55.5 -40.4 -25.3 -10.3 -0.2 10.2 32.8 36.9 41.0 45.1 49.3 53.4 57.5 61.6 65.7 69.8 32.8 36.9 41.0 45.1 49.3 53.4 57.5 61.6 65.7 69.8

0.9 1.2 12.9 16.6 18.9 21.5 23.7 25.0 10.5 13.5 16.4 19.3 22.2 25.1 28.1 31.0 33.9 36.8 10.5 13.5 16.4 19.3 22.2 25.1 28.1 31.0 33.9 36.8

Percent

I, 2: lateral to ovoids; 3-9: anterior 10-28: lateral to vaginal catheter.

102 102 105 108 105 103 110 122 107 103 103 105 108 110 111 110 104 95 107 103 103 105 108 110 111 110 105 95

dose points

axes (mm) cGy

Description

850

point A

axes (mm) cGy 863 863 895 922 889 873 932 1035 908 879 879 895 918 939 947 932 884 803 905 876 875 891 915 936 947 934 890 811

to intrauterine

Description 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Volume 29, Number 4, 1994

brachytherapy sources. Until now, no comparable applicator exists in HDR brachytherapy. We, therefore, constructed a teflon vaginal cylinder to use with the existing applicator as developed in Rotterdam to assure a constant distance between the vaginal section of the intrauterine tube and the vaginal wall. By defining dwell positions in this part of the tube (position 17-28, Table 2) and using the optimization program of the Nucletron Planning System, isodose patterns were calculated to apply adequate radiation to all known tumor in these cases, by using a single applicator type for two fractions HDR-brachytherapy. The dose distribution at the rectal wall, near the sigmoid colon, and near the small bowel as achieved by the optimization program for the adapted applicator, was comparable with the isodose curves of the existing applicator. The bladder dose, however, was found to be increased by about 10% when using the adapted applicator (dose in dose point no. 8, Table 1). However, we do not expect this to result in bladder complications, because the bladder dose remains well below the tolerance level of 1 1 Gy per fraction ( 1,2). In this way, adequate HDR-brachytherapy can be applied safely in patients with cervical carcinoma extending to the vagina and the parametria.

Table 2. Dwell time table Catheter Pos.

Weight

l--l--l 2 0.65 0.62 3 4 0.58

Catheter

1

Catheter

Sec.

Pos.

Weight

Sec.

Pos.

80.6 76.5 71.0

2 3 4

0.66 0.62 0.57

81.2 76.5 70.2

2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

catheter;

consisted of a first application of 8.5 Gy to point A with an applicator developed in Rotterdam, consisting of an intrauterine tube, two ovoids, a monodenticular tenaculum, and a rectal retractor. After this, a second application of 8.0 Gy at 5 mm depth from the vaginal surface was given with the same intrauterine tube (without ovoids) and a vaginal cylinder. In this way, only the intrauterine part of the target volume is irradiated adequately, because the vagina, as well as the parametria, are irradiated only once, resulting in an inadequate dose as applied by brachytherapy. Moreover, combining two different sets of applicators inevitably leads to unknown zones of overor underdosage due to the anatomical inconsistency between both applicators. The first applicator designed to irradiate all known tumor in cervical tumors with parametrial and vaginal extension in one application was developed by Perez et al. (4), using low dose rate (LDR)

2

Pos. = position;

sec. = seconds.

Weight 0.36 0.35 0.33 0.32 0.32 0.33 0.32 0.30 0.26 0.19 0.12 0.05 0.04 0.10 0.17 0.23 0.28 0.33 0.39 0.47 0.59 0.74 0.91

1.oo

3 Sec. 44.3 43.1 40.1 38.8 39.4 40.4 40.0 37.1 31.5 23.7 14.8 6.5 5.3 12.7 20.5 27.8 34.3 40.5 47.7 57.8 72.4 91.6 112.0 123.1

Brachytherapy for cervical cancer 0 C. G. J. H. NI~~Lelal.

877

Fig. 4. Dose distribution: plane 1-sagittal through intrauterine and vaginal catheter. Plane 2-frontal plane through vaginal dose points. Plane 3-rotated frontal plane through ovoids and through intrauterine catheter.

CONCLUSION Brachytherapy in the DDHCC for cervical carcinoma extending to the vagina and the parametria was up to now unsatisfactory due to inadequate irradiation doses to the

vagina and the parametria when combining different sets of applicators. We, therefore, adapted the existing HDR applicator as developed in Rotterdam to apply fractionated brachytherapy with one applicator type to all known tumor to an adequate dose level.

REFERENCES Kuipers, Tj. Cervix carcinoma, results of external irradiation combined with brachytherapy, highdose-rate versus lowdose-rate. In: Mould, R. F.; Tungsubutra, K., eds. Diagnosis and treatment of carcinoma of the cervix in developing areas. Proceedings of the meeting of the International working Party and International conference on diagnosis and treatment of carcinoma of the cervix in developing areas. Bristol: Adam Hilger Ltd.; 1985:169-176. Kuipers, Tj. High dose rate afterloading in the treatment of cervix carcinoma with external irradiation and brachytherapy. In: Radiotherapy in developing countries. Proceedings symposium organized by the International Atomic Energy Agency, Vienna, l-5 September 1986. Vienna: IAEA-SM290/13; 1987:27-31. Perez, C. A.; Breaux, S.; Madoc-Jones, H.; Bedwinek, J. M.;

Camel, M.; Purdy, J.; Walz, B. J. Radiation therapy alone in the treatment of carcinoma of the uterine cervix. I: Analysis of tumor recurrence. Cancer 5 1: 1393- 1404; 1983. Perez, C. A.; Slessinger, E.; Grigsby P. W. Design of an afterloading vaginal applicator (MIRALVA). Int. J. Radiat. Oncol. Biol. Phys. 18: 1503- 1508; 1990. Subandono-Tjokrowardojo, A. J.; Kuipers, Tj.; Koper, P. C. M.; Veeze-Kuipers, B.; Visser, A. G.; Star, W. Application of the selectron HDR in the treatment of gynecological tumours: The Rotterdam method. Activity (Select. Brachyther. J.) 4:93-99; 1990. Tod, M. C.; Meredith, W. J. A dosage system for use in the treatment of cancer of the uterine cervix. Br. J. Radiol. 11: 809-824; 1938.